line for a specially enabled audio interface to interpret. Using the output from the MICPWR pin, the external

microphone can be biased directly or through an external circuit as shown in Figure 8-1.

During a typical application where IMICPWR falls between 120µA and 150µA, the MICPWR pin provides a voltage

from 1.51V to 1.61V (1.56V typical, see VMICPWR). Leaving the MICPWR pin floating or drawing current outside

of these limits results in voltage exceeding the MICPWR output voltage specifications. Additionally, increasing

the voltage on the MIC pin above 2.5V drives the MICPWR output voltage above 1.61V.

Power up

Button mode

switch A open

switch B closed

VMIC > 2.3V?

N

Y

Debounce?

N

Y

Press S0?

N

Y

Open switch B

Close switch A

Send

ACK tone

Tone mode

switch A closed

switch B open

Button

press

(S0)?

Button press

(S1, S2,

S3,or S4)?

Y

N

Y

Send

button

tone

N

Figure 7-5. Tone Mode Power-up Sequence

For accuracy, the CD326x transmits two tones for each button press as shown in Figure 7-6. The first tone is

enabled for a period of 0.9ms and is a calibration frequency. The second tone is enabled for a period of 1.8ms

and is the unique frequency for the selected button. The specially enabled audio interface calculates the ratio of

these two frequencies and translates the ratio into button press information. This functionality provides accurate

results independent of clock frequency variation.

CD3268A, CD3269A

SCHS463 – MAY 2025

www.ti.com

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